The present invention relates to head-gimbal assemblies for reading and writing magnetically encoded information. In particular, the invention relates to routing and supporting a conductor sleeve running from a head to a support arm of the head-gimbal assembly.
A head-gimbal assembly (HGA) used in a hard disc file includes essentially three components. The first component is a slider which features a self-acting hydrodynamic air bearing and an electromagnetic transducer used for recording and retrieving information from a spinning magnetic disc.
The second component is a gimbal which is attached to the slider. The gimbal is resilient in the slider's pitch and roll directions to allow the slider to follow the topography of the disc over which it is flying. Also, the gimbal is rigid in the in-plane directions for maintaining precise in-plane slider positioning.
The third component is a load beam which is attached to the gimbal and to a support arm. The load beam is typically connected to the support arm by a well-known technique referred to as "swaging" or "ball staking". The load beam is resilient in the vertical direction to allow the slider to follow the topography of the disc. As with the gimbal, the load beam is rigid in the in-plane directions. The load beam also acts as a spring, supplying a downward force that counteracts the hydrodynamic lifting force developed by the air bearing.
Electrical signals are sent to and received from the electromagnetic transducer by very small conductors. The conductors are typically twisted copper wires. There are usually two conductors, but the number of conductors may vary.
These conductors are threaded through a hollow sleeve, typically made of flexible polytetrafloroethylene (PTFE) tubing, to prevent damage to the conductors. Traditionally, this conductor sleeve was routed along the back of the load beam, between two support rails. The tubing would extend to the far end of the gimbal, proximate the electromagnetic transducer, and the conductor wires would then loop over the end of the HGA to termination pads on the slider.
As the physical size of disc files has grown progressively smaller, however, the traditional routing method is no longer feasible. The advent of reverse rail suspensions on modern load beams has necessitated very close back-to-back clearances in order to deflect the load beams and load HGAs into the drives. In fact, to date this has resulted in nearly a 30% reduction in overall disc-to-disc space. In light of this reduction, the conductor sleeve consumes too much space when routed along the back of the load beam. Therefore, a new method for routing the conductor sleeve has become necessary.
Initial attempts to reroute the conductor sleeve along the top surface of the load beam have been largely unsuccessful. Adhesives do not attach well to PTFE. Because PTFE is the preferred material for the conductor sleeve, the use of adhesives to fix the conductor sleeve is difficult. In addition, tacking down both ends of the conductor sleeve to the load beam may lead to undesirable deformation of the sleeve and wire. Temperature changes during cleaning operations or in transit can cause expansion or contraction of the PTFE sleeve. If both ends of the sleeve are secured along the load beam's surface, the conductor sleeve may subsequently stretch or "bow" outward, leading to possible damage to the sleeve or the HGA.
The most serious problem with routing the sleeve along the top of the load beam, however, is the unusually long distance the bare conductor wires must run from the end of the PTFE tubing to the slider assembly. The sharp, etched edges of the HGA could cause damage to the conductor wires. Attempts to tack down the bare wire also pose difficulties with the gimbal's hydrodynamics, as well as its production consistency.
Those skilled in the art are generally reluctant to alter the structure of the gimbal itself. The hydrodynamic characteristics of the gimbal are extremely sensitive, and even the slightest alterations to any part of the assembly can render the HGA inoperable. Therefore, there is a continuing need for effective and efficient methods of routing the conductor sleeve along the HGA, consistent with the present space constrictions and gimbal performance parameters.